Multimedia Broadcast/Multicast Services (MBMS) over wireless networks, such as cellular radio network are becoming widely spread, especially after that mobile handheld devices became capable of receiving multimedia content via radio networks. E-MBMS was introduced in the Release 8 of 3GPP standard for long term evolution (LTE) in order to deliver multimedia data from a single source entity to multiple destinations in LTE. An overview of the MBMS system is given in chapter 15 in the 3GPP technical specification TS 36.300.
While embodiments are described below in relation to Multimedia Broadcast Multicast Service (MBMS) as implemented in LTE, the invention finds application also in other cellular radio networks such as WCDMA, GSM, CDMA etc, but may also be applicable in other type of networks implementing broadcast services. The MBMS that is implemented in LTE and its advance is called Evolved-Multimedia Broadcast Multicast Service (E-MBMS) and is considered as an important component in the LTE architecture.
The MBMS provides two different services: Broadcast and multicast services. The Broadcast service may be received by any subscriber in the area in which the service is offered and multicast services may only be received by users having subscribed to the service and having joined the multicast group associated with the service. Both these services are point to multipoint transmissions of multimedia data and may be highly applied to broadcast text, audio, picture and video to any user located in the service area.
Now, the necessary functions to support E-MBMS in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) also sometimes referred to as LTE networks are being discussed and defined in the 3GPP standardization body. An important difference compared the MBMS delivery in an Universal Terrestrial Radio Access Network (UTRAN) comes from the distributed nature of E-UTRAN architecture. In E-UTRAN the radio resource management functions, including the scheduling are located in the evolved NodeBs (eNBs), i.e. in the base stations as opposed to UTRAN, Where the radio resource control is located centrally in the Radio Network Controller (RNC). Therefore for MBMS transmission, which may require coordinated and time synchronized transmission from multiple cells, i.e. called Multi Broadcast Single frequency Network (MBSFN) transmission, additional central control entities like the MBMS Control Entity (MCE) have been added to the architecture.
In FIG. 1 the E-MBMS area concept in the LTE networks is discussed. The area 100 of the network where all eNBs can be synchronized and perform MBSFN transmissions is defined as MBSFN Synchronization Area 100. The MBSFN Synchronization Area 100 consists of a number of MBSFN Areas 101. The MBSFN Area 101 is a group of cells within an MBSFN Synchronization Area of a network, which are coordinated to achieve an MBSFN Transmission. A MBSFN Area Reserved Cell 102 is defined as a cell within a MBSFN Area 101 which does not contribute to the MBSFN Transmission.
For the transport of MBMS data over the radio interface two logical channels are introduced into the LTE standard, the MBMS Control channel (MCCH) and the MBMS Traffic Channel (MTCH). The MCCH and MTCH logical channels are mapped onto the MCH transport channel as shown in FIG. 2. Optionally and depending on transmission mode and resource control, it may be possible to map these logical channels to the normal downlink shared channel (DL-SCH) used to deliver the unicast traffic as well. The MTCH channel carries the actual MBMS data while the MCCH carries control information necessary for the reception of the MTCH channel.
Based on the MBMS area definition, the standard defines two main transmission mode of a cell to deliver MBMS content in LTE networks. These are:
Multi-cell transmission: in this transmission mode the same multimedia content is transmitted in multiple cells within an MBSFN Area 101 in a time synchronized fashion, such that the physical signals arriving from different cells at the User Equipment (UE) can be soft combined. Fixed Resource Blocks (RBs) with long cyclic prefix (CP) called MBSFN RBs are assigned to the MBMS service in these cells. The MBMS transmission from the multiple cells is seen as from one source by the UE. In this mode, the MTCH and MCCH are mapped on MCH for a Point to Multipoint (PTM) transmission, and all cells within the MBSFN area, except the MBSFN area reserved cell 102, contribute to the MBSFN transmission.
Single-cell transmission: In this mode the transmission in a cell is targeted only for the user in the given cell. The cell is an MBSFN area reserved cell 102 and there is no coordination of the transmission from multiple cells. In other words, cells in this transmission mode do not take part in any synchronous transmission. The eNB on its own can decide how to allocate radio resource to deliver the MBMS service, i.e. it is able to perform scheduling. In this mode, the MTCH and the MCCH may be transmitted on the DL-SCH or the MCH.
It is today difficult or almost impossible to configure one cell as reserved cell statically, except for those cells which are determined that they will not provide MBMS service to the UEs 302, 405, 406.
If all cells within an MBSFN area 101 are in one transmission mode, the goal to reach an efficient radio resource allocation for all cells is impossible to be fulfilled due to the complexity of the wireless environment and the user service profile. For example in FIG. 3, the serving cell, C31, is working in a multi-cell transmission mode and the UEs 302 receiving MBMS data are located near the base station (eNB) 301 and scarcely receives any MBSFN transmission from neighboring cells. Hence the gain at the UEs 302 of combining signals arriving from neighboring cells taking part in the synchronous transmission is almost zero. Furthermore, under this situation, MBSFN transmission leads to bad spectrum efficiency due to long CP and none of Hybrid Automatic Repeat Request (HARQ), adaptive modulation. In other words, as the quality of radio link is good, eNB 301 may provide the same MBMS service with less RBs if the MTCH and the MCCH are mapped to a DL-SCH. Based on the above, it is clear that the serving cell, C31, should have been in a single-cell transmission mode to achieve an efficient radio resource allocation.
In another example as shown in FIG. 4, the MBMS transmission is executed from a time-synchronized set of eNBs 401, 402, 403 using the same RBs. This enables over-the-air combining of the signals at the cell edge located UEs 405, 406 thus improving the SINR of MBMS service significantly for those UEs 405, 406 at the cell edge. As shown in FIG. 4, if one cell, C41, only has UEs 405 at cell edge requiring MBMS service, it is very likely that MBMS signals arriving from neighboring cells, C42, C43, are good enough to provide MBMS service for those UEs 405. Consequently, this cell, C41, could efficiently stop multi-cell transmission and use the reserved RBs for MBSFN to perform other services. However existing solutions does not allow switching from one transmission mode to another to achieve an efficient radio resource allocation.
Hence, current MBMS transmission mechanism leads to an inefficient radio resource usage. There is a constant demand to increase the efficiency of a radio system and to utilize existing resources in an optimal way.